The series follows two women, modern-day archeologist Alice Tanner and medieval Alaïs Pelletier du Mas who lives through the Crusades and Cathar massacres in medieval France—and their quest to find the Holy Grail. Alice, a volunteer at a French archaeological excavation, discovers the skeletal remains of two people in a cave, as well as a labyrinth-engraved ring, which attracts the attention of unscrupulous individuals. In 1209, newly married Alaïs is living in Carcassonne, a stronghold of Cathars who have been declared heretical by the Church. Alaïs and her father are protecting three sacred books that reveal the secret of the Holy Grail from the Crusaders